JP2011065838A - Membrane electrode assembly for solid-polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly for solid-polymer fuel cell capable of attaining high power-generating characteristic under high temperature and low-humidified or non-humidified operating condition compared with conventional assemblies. <P>SOLUTION: The membrane electrode assembly for the solid-polymer fuel cell has an anode 13 and a cathode 14 both having a catalytic layer 11 containing solid-polymer electrolytic polymer, and a high-polymer electrolytic film 15 disposed in between the anode 13 and the cathode 14. The catalytic layer 11 of the cathode 14 contains as the solid-polymer electrolytic polymer a polymer (H) corresponding to a dry resin with 0.9 to 2.5 mm equivalent/g ion-exchange capacity, has an oxygen-permeability coefficient of ≥1×10<SP>-12</SP>[cm<SP>3</SP>(Normal)×cm/cm<SP>2</SP>×s×Pa] when measured at 100°C by means of high-vacuum method, and has oxygen/nitrogen separation coefficient ≥2.5 at 100°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a membrane electrode assembly for a polymer electrolyte fuel cell.

  In the polymer electrolyte fuel cell, for example, a cell is formed by sandwiching a membrane electrode assembly between two separators, and a plurality of cells are stacked. The membrane electrode assembly includes an anode and a cathode having a catalyst layer, and a solid polymer electrolyte membrane disposed between the anode and the cathode. The catalyst layer is a catalyst in which platinum fine particles are supported on carbon. And a solid polyelectrolyte polymer.

As the solid polymer electrolyte polymer, the following polymer (1) is well known.
A —SO ₂ F group of a polymer having a repeating unit based on the compound represented by the following formula (m1) and a repeating unit based on tetrafluoroethylene (hereinafter referred to as TFE) is converted to a sulfonic acid group (—SO ₃ H group). ) Converted to (1).
_{CF 2 = CF (OCF 2 CFZ} ) m O p (CF 2) n SO 2 F ··· (m1).
However, Z is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, p is 0 or 1, n is 1 to 12, and m + p> 0.

  In the polymer electrolyte fuel cell, in order to simplify the fuel cell system and reduce the cost, the reaction gas (fuel gas and oxidant gas) has a low relative humidity or low humidification condition (for example, solid polymer) There is a demand for operation in which the relative humidity of the oxidant gas supplied to the fuel cell is 30% or less at the temperature in the polymer electrolyte fuel cell. Further, in order to improve the power generation voltage and power generation efficiency, operation at a higher temperature (for example, the temperature in the polymer electrolyte fuel cell is 90 to 140 ° C.) is required.

The reaction in the polymer electrolyte fuel cell is represented by the following formulas (R1) and (R2). It is said that the reaction at the cathode represented by the formula (R2) is rate-limiting, and in order to promote the reaction, it is necessary to increase the proton concentration and the oxygen concentration in the reaction field.
Anode: H ₂ → 2H ⁺ + 2e ⁻ (R1),
Cathode: 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (R2).

  Therefore, in order to exhibit sufficient power generation characteristics (output voltage, etc.) under high temperature and low or no humidification conditions, the ion exchange capacity of the solid polymer electrolyte polymer is increased and oxygen permeability at high temperature is also achieved. Need to be increased. Normally, the gas permeability of a polymer becomes higher at a high temperature. Therefore, if the solid polymer electrolyte polymer has a certain degree of gas permeability, sufficient oxygen permeability at a high temperature can be obtained.

  Further, since air is normally supplied to the cathode, when the oxygen / nitrogen separation coefficient of the solid polymer electrolyte polymer is high, a higher concentration of oxygen is supplied to the reaction field, and higher power generation characteristics can be obtained.

In an attempt to increase the oxygen concentration at the cathode, the oxygen transmission coefficient measured at 25 ° C. by a high vacuum method is 5 × 10 ⁻¹¹ [cm ³ (Normal) · cm / cm ² · s · Pa] or more. In addition, it has been proposed to include a polymer compound having no ion exchange group in the catalyst layer (Patent Document 1).

  However, although the polymer compound has high oxygen permeability but does not have an ion exchange group, the concentration of the ion exchange group in the catalyst layer decreases, and the proton concentration cannot be increased. In particular, there is a problem that power generation characteristics cannot be sufficiently exhibited in operation under low or no humidification conditions.

As a means for solving this problem, the oxygen permeability coefficient measured by the isobaric gas chromatography method at a temperature of 80 ° C. and a relative humidity of 80% is 5 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s. It has been proposed that the catalyst layer contains a fluorine-containing ion exchange resin that is equal to or greater than Pa] (Patent Document 2).

  However, the value of the oxygen transmission coefficient is a value at a relatively high humidification temperature of 80 ° C. and a relative humidity of 80%. Is it possible to obtain sufficient power generation characteristics in operation at higher temperatures and low humidification conditions? Whether it is unknown. Moreover, examination about oxygen / nitrogen separability is not made | formed.

JP 2002-252001 A JP 2003-036856 A

  The present invention provides a membrane / electrode assembly for a polymer electrolyte fuel cell, which can obtain higher power generation characteristics under operating conditions of high temperature and low or no humidification compared to conventional ones.

A membrane electrode assembly for a polymer electrolyte fuel cell according to the present invention includes an anode having a catalyst layer containing a solid polymer electrolyte polymer, a cathode having a catalyst layer containing a solid polymer electrolyte polymer, the anode and the cathode, A polymer electrolyte membrane disposed between the cathode and the catalyst layer of the cathode, as the solid polymer electrolyte polymer, having an ion exchange capacity of 0.9 to 2.5 meq / g dry resin, Oxygen permeation coefficient measured at a temperature of 100 ° C. by a vacuum method is 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more and an oxygen / nitrogen separation factor of 100 ° C. It contains the polymer (H) whose is 2.5 or more.

The polymer (H) has a cyclic structure and a repeating unit (A) not having an ion exchange group or a precursor group thereof, and / or a cyclic structure and an ion exchange group or a precursor group thereof. The total proportion of the repeating unit (A) and the repeating unit (B) is 20 mol% or more among all repeating units in the polymer (H). preferable.
The cathode catalyst layer is preferably heat treated at a temperature of 150 to 180 ° C. for 1 to 60 minutes.

  The membrane / electrode assembly for a polymer electrolyte fuel cell of the present invention can obtain high power generation characteristics under high temperature and low or non-humidified operating conditions as compared with the conventional one.

It is sectional drawing which shows an example of the membrane electrode assembly of this invention. It is sectional drawing which shows the other example of the membrane electrode assembly of this invention.

In this specification, the repeating unit represented by the formula (U1) is referred to as a unit (U1). Repeating units represented by other formulas are also described in the same manner.
Moreover, in this specification, the compound represented by a formula (M1-1) is described as a compound (M1-1). The same applies to compounds represented by other formulas.

The repeating unit in the present invention means a unit derived from the monomer formed by polymerization of the monomer. The repeating unit may be a unit directly formed by a polymerization reaction, or may be a unit in which a part of the unit is converted into another structure by treating the polymer.
The monomer in the present invention means a compound having a polymerization-reactive carbon-carbon double bond.

The ion exchange group in the present invention means a group having H ⁺ , monovalent metal cation, ammonium ion and the like. Examples of the ion exchange group include a sulfonic acid group, a sulfonimide group, and a sulfonemethide group.
The precursor group in the present invention means a group that can be converted into an ion exchange group by a known treatment such as hydrolysis treatment or acidification treatment. Examples of the precursor group include —SO ₂ F group.

<Membrane electrode assembly>
FIG. 1 is a cross-sectional view showing an example of a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter referred to as a membrane electrode assembly).
The membrane electrode assembly 10 includes an anode 13 having a catalyst layer 11 and a gas diffusion layer 12 containing a solid polymer electrolyte polymer, a cathode 14 having a catalyst layer 11 and a gas diffusion layer 12 containing a solid polymer electrolyte polymer, and an anode A solid polymer electrolyte membrane 15 disposed in contact with the catalyst layer 11 is provided between the cathode 13 and the cathode 14.

In the present invention, the catalyst layer 11 of the cathode 14 is a dry polymer having an ion exchange capacity of 0.9 to 2.5 meq / g as a solid polymer electrolyte polymer, and a temperature of 100 ° C. in a high vacuum method. A polymer having an oxygen permeation coefficient of 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more and an oxygen / nitrogen separation coefficient of 2.5 or more at 100 ° C. H) is included.

(Polymer (H))
The ion exchange capacity of the polymer (H) is 0.9 to 2.5 meq / g dry resin. When the ion exchange capacity is 0.9 meq / g dry resin or more, proton conductivity under low or no humidification conditions does not become too low. If the ion exchange capacity is 2.5 meq / g dry resin or less, the degree of swelling of the polymer (H) will not be too high. Therefore, the generated water does not cause flooding and hinder the supply of air, and the polymer (H) does not dissolve in the generated water. The ion exchange capacity is preferably 1.0 to 2.2 meq / g dry resin from the viewpoint that proton conductivity can be secured under low or no humidification conditions and excessive swelling does not occur. From the point suitable for humidification conditions, 1.6 to 2.0 meq / g dry resin is more preferable.

The oxygen permeability coefficient of the polymer (H) is 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more. When the oxygen permeability coefficient is 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more, the oxygen concentration in the reaction field becomes high and the reaction easily proceeds. The oxygen permeability coefficient is preferably 3 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more, and preferably 5 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa]. The above is more preferable. The upper limit of the oxygen permeability coefficient is not particularly limited, but a solid having an oxygen permeability coefficient of 5 × 10 ⁻¹¹ [cm ³ (Normal) · cm / cm ² · s · Pa] or more while ensuring proton conductivity. Since it is difficult to synthesize a polyelectrolyte polymer, it is usually less than 5 × 10 ⁻¹¹ [cm ³ (Normal) · cm / cm ² · s · Pa].

  The oxygen permeation coefficient in the present invention is an oxygen permeation coefficient of a cast film measured on the condition of a temperature of 100 ° C. based on a high vacuum method by setting a cast film produced from a solid polymer electrolyte polymer in a gas permeation measuring apparatus.

  The oxygen / nitrogen separation coefficient at 100 ° C. of the polymer (H) is 2.5 or more, preferably 2.7 or more, and more preferably 3.0 or more. When the oxygen / nitrogen separation coefficient at 100 ° C. is 2.5 or more, the oxygen concentration in the reaction field is sufficiently increased, and the power generation characteristics are improved.

  The oxygen / nitrogen separation factor at 100 ° C. in the present invention is determined by setting the cast membrane prepared from the solid polymer electrolyte polymer in a gas permeation measuring device and measuring the oxygen in the cast membrane based on the high vacuum method at a temperature of 100 ° C. It is the ratio between the permeability coefficient and the nitrogen permeability coefficient.

The mass average molecular weight of the polymer (H) is preferably 1 × 10 ⁴ to 1 × 10 ^7, more preferably 5 × 10 ^{4 to} 5 × 10 ⁶ , and even more preferably 1 × 10 ^{5 to} 3 × 10 ⁶ . When the mass average molecular weight of the polymer (H) is 1 × 10 ⁴ or more, physical properties such as the degree of swelling hardly change with time, and durability is sufficient. If the polymer (H) has a mass average molecular weight of 1 × 10 ⁷ or less, solutionization and molding become easy.

The mass average molecular weight of the solid polymer electrolyte polymer can be evaluated by measuring the TQ value. The TQ value (unit: ° C.) is an index of the molecular weight of the polymer. The extrusion amount when the polymer is melt-extruded under the condition of the extrusion pressure of 2.94 MPa using a nozzle having a length of 1 mm and an inner diameter of 1 mm is 100 mm. ^The temperature is ³ / sec. For example, a polymer having a TQ value of 200 to 300 ° C. corresponds to a mass average molecular weight of 1 × 10 ⁵ to 1 × 10 ⁶ although the composition of repeating units constituting the polymer differs.

  The polymer (H) includes a repeating unit (A) having a cyclic structure and not having an ion exchange group or a precursor group thereof, and / or having a cyclic structure and an ion exchange group or a precursor group thereof. The polymer (H1) having the repeating unit (B) having is preferable. The polymer (H1) having a repeating unit having a cyclic structure in the main chain exhibits high oxygen permeability and high oxygen / nitrogen separation characteristics at high temperatures.

  The polymer (H1) does not have a cyclic structure, and may have a repeating unit (C) having an ion exchange group or a precursor group thereof, and / or another repeating unit (D) as necessary. .

  The ratio of the total of the repeating unit (A) and the repeating unit (B) (hereinafter, collectively referred to as a repeating unit having a cyclic structure) out of all repeating units in the polymer (H1) is 20 mol%. That's it. The proportion of the repeating unit having a cyclic structure is preferably 40 mol% or more, more preferably 60 mol% or more, from the viewpoint of high oxygen permeability coefficient and oxygen / nitrogen separation coefficient at high temperatures, although it varies depending on the type of cyclic structure. .

Repeating unit (A):
As the repeating unit (A), units (U1) to (U4) are preferable.

However, c is an integer from 1 to ^4, R 1, R ² are each independently a fluorine atom or a trifluoromethyl group, R ³ is a perfluoroalkyl group or a perfluoroalkoxy group having 1 to 8 carbon atoms.
The units (U1) to (U4) are preferably 4- to 7-membered rings, and more preferably 5-membered or 6-membered rings from the viewpoint of ring stability.

  As the monomer (a) that can constitute the repeating unit (A), a monomer (a1) that has a cyclic structure and does not have an ion exchange group or a precursor group thereof, or an ion exchange group or a precursor group thereof. And a cyclopolymerizable monomer (hereinafter referred to as monomer (a2)) capable of forming a cyclic structure simultaneously with polymerization.

  As the monomer (a1), perfluoro (2,2-dimethyl-1,3-dioxole) (hereinafter referred to as PDD), perfluoro (1,3-dioxole), perfluoro (2-methylene-4-methyl-1). , 3-dioxolane) (hereinafter referred to as MMD), 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole and the like.

  As the monomer (a2), perfluoro (3-butenyl vinyl ether) (hereinafter referred to as BVE), perfluoro [(1-methyl-3-butenyl) vinyl ether], perfluoro (allyl vinyl ether), 1,1 ′-[ (Difluoromethylene) bis (oxy)] bis [1,2,2-trifluoroethylene] and the like.

  Specific examples of the repeating unit based on the monomer (a1) or the monomer (a2) include a repeating unit based on PDD (U1-1), a repeating unit based on BVE (U3-1), a repeating unit based on MMD (U4-1) ) And the like.

Repeating unit (B):
As the repeating unit (B), the unit (U5) is preferable.

However, R ¹¹ is a divalent perfluoro organic group that may have an etheric oxygen atom, and R ¹² , R ¹³ , R ¹⁵ , and R ¹⁶ each independently have an etheric oxygen atom. R ¹⁴ may be a monovalent perfluoro organic group which may have an ether bond oxygen atom, a fluorine atom, or —R ¹¹ (SO ₂ X (SO ₂ R ^f ) _d ) ⁻ M ⁺ group, R ^f is a perfluoroalkyl group optionally having an etheric oxygen atom, X is an oxygen atom, a nitrogen atom or a carbon atom, d Is 0 when X is an oxygen atom, 1 when X is a nitrogen atom, 2 when X is a carbon atom, and M ⁺ is H ⁺ , a monovalent metal cation, or one or more hydrogen Atom replaced with hydrocarbon group Also be a good ammonium ion.

  As the unit (U5), the unit (U5-1) is particularly preferable from the viewpoint of easy synthesis of a monomer capable of constituting the unit (U5) and high polymerization reactivity.

Repeating unit (C):
The repeating unit (C), the repeating units obtained by converting the -SO 2 _F groups of the repeating units based on perfluorovinyl ether having a -SO 2 _F group in the acidic group. Specifically, the unit (U6) or the unit (U7) is preferable.

However, Q ¹ is a perfluoroalkylene group which may have an ether bond oxygen atom, Q ² is a perfluoroalkylene group which may have a single bond or an ether bond oxygen atom, R ^f1 is a perfluoroalkyl group which may have an etheric oxygen atom, X ¹ is an oxygen atom, a nitrogen atom or a carbon atom, and a is 0 when X ¹ is an oxygen atom , ¹ when X ¹ is a nitrogen atom, 2 when X ¹ is a carbon atom, Y ¹ is a fluorine atom or a monovalent perfluoro organic group, s is 0 or 1,
Q ³ is a single bond or a perfluoroalkylene group optionally having an etheric oxygen atom, R ^f2 is a perfluoroalkyl group optionally having an etheric oxygen atom, and X ² Is an oxygen atom, a nitrogen atom or a carbon atom, b is 0 when X ² is an oxygen atom, 1 when X ² is a nitrogen atom, ² when X ² is a carbon atom, Y ² is a fluorine atom or a monovalent perfluoro organic group, and t is 0 or 1.
The single bond means that the carbon atom of CY ¹ or CY ² and the sulfur atom of SO ₂ are directly bonded.
An organic group means a group containing one or more carbon atoms.

Unit (U6):
When the perfluoroalkylene group of Q ¹ and Q ² has an etheric oxygen atom, the oxygen atom may be one or two or more. The oxygen atom may be inserted between the carbon atom-carbon atom bonds of the perfluoroalkylene group or may be inserted at the carbon atom bond terminal.
The perfluoroalkylene group may be linear or branched, and is preferably linear.
1-6 are preferable and, as for carbon number of a perfluoroalkylene group, 1-4 are more preferable. When the number of carbon atoms is 6 or less, the boiling point of the monomer that can constitute the unit (U6) becomes low, and distillation purification becomes easy. Moreover, if carbon number is 6 or less, the increase in the equivalent weight of a polymer (H1) will be suppressed, and the proton conductivity fall will be suppressed.

Q ² is preferably a C 1-6 perfluoroalkylene group which may have an etheric oxygen atom. When Q ² is a C 1-6 perfluoroalkylene group which may have an etheric oxygen atom, the polymer electrolyte fuel cell was operated over a longer period than when Q ² is a single bond. In particular, the stability of power generation characteristics is excellent.
At least one of Q ¹ and Q ² is preferably a C 1-6 perfluoroalkylene group having an etheric oxygen atom. Since a fluorine-containing monomer having a C 1-6 perfluoroalkylene group having an etheric oxygen atom can be synthesized without undergoing a fluorination reaction with a fluorine gas, the yield is good and the production is easy.

The perfluoroalkyl group for R ^f1 may be linear or branched, and is preferably linear.
1-6 are preferable and, as for carbon number of a perfluoroalkyl group, 1-4 are more preferable. As the perfluoroalkyl group, a trifluoromethyl group or a pentafluoroethyl group is preferable.
When the unit (U6) has two or more R ^{f1 s} , R ^f1 may be the same group or different groups.

_{^{- (SO 2 X 1 (SO}} 2 R f1) a) - H + group is an ion-exchange group.
_{^{- (SO 2 X 1 (SO}} 2 R f1) a) - The ^{H +} group, a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group ^{_{(-SO 2 N (SO 2 R}} f1) - H ⁺ group), or a sulfonmethide group ^{_{(-SO 2 C (SO 2 R}} f1) 2) - H + group).
Y ¹ is preferably a fluorine atom or a linear perfluoroalkyl group having 1 to 6 carbon atoms which may have an etheric oxygen atom.

  As the unit (U6), the unit (U6-1) is preferable, and the unit (U6-11) and the unit (U6-12) are preferable because the production of the polymer (H1) is easy and the industrial implementation is easy. Or a unit (U6-13) is more preferable.

However, R ^<F11> is a C1-C6 linear perfluoroalkylene group which may have a single bond or an ether bond oxygen atom, and R ^<F12> is a C1-C6 linear chain Perfluoroalkylene group.

Unit (U7):
When the perfluoroalkylene group of Q ³ has an etheric oxygen atom, the oxygen atom may be 1 or 2 or more. The oxygen atom may be inserted between the carbon atom-carbon atom bonds of the perfluoroalkylene group or may be inserted at the carbon atom bond terminal.
The perfluoroalkylene group may be linear or branched.
1-6 are preferable and, as for carbon number of a perfluoroalkylene group, 1-4 are more preferable. When the number of carbon atoms is 6 or less, an increase in the equivalent weight of the polymer (H1) can be suppressed, and a decrease in proton conductivity can be suppressed.

The perfluoroalkyl group for R ^f2 may be linear or branched, and is preferably linear.
1-6 are preferable and, as for carbon number of a perfluoroalkyl group, 1-4 are more preferable. As the perfluoroalkyl group, a trifluoromethyl group or a pentafluoroethyl group is preferable.

_{^{- (SO 2 X 2 (SO}} 2 R f2) b) - H + group is an ion-exchange group.
_{^{- (SO 2 X 2 (SO}} 2 R f2) b) - as the ^{H +} group, a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group ^{_{(-SO 2 N (SO 2 R}} f2) - H ⁺ group), or a sulfonmethide group ^{_{(-SO 2 C (SO 2 R}} f2) 2) - H + group).
Y ² is preferably a fluorine atom or a trifluoromethyl group.

  As the unit (U7), the unit (U7-1) is preferable. From the viewpoint of easy production of the polymer (H1) and easy industrial implementation, the unit (U7-11) and the unit (U7-12) are preferred. , Unit (U7-13) or unit (U7-14) is more preferred.

  However, Z is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, p is 0 or 1, n is an integer of 1 to 12, and m + p> 0. is there.

Repeat unit (D):
The repeating unit (D) is preferably a repeating unit based on a perfluoromonomer and more preferably a repeating unit based on TFE from the viewpoint of mechanical strength and chemical durability.
The ratio of the repeating unit based on TFE is not particularly limited, but may be appropriately adjusted so that the equivalent weight of the polymer (H1) falls within a preferable range.

(Catalyst layer)
The catalyst layer 11 includes a solid polymer electrolyte polymer and a catalyst.
Examples of the catalyst include a supported catalyst in which platinum or a platinum alloy is supported on a carbon support.
Examples of the carbon carrier include carbon black powder. From the viewpoint of durability, carbon black powder graphitized by heat treatment or the like is preferable.

  The mass ratio of the catalyst to the solid polymer electrolyte polymer (catalyst / solid polymer electrolyte polymer) in the catalyst layer 11 is preferably 5/5 to 9.5 / 0.5 from the viewpoint of conductivity and water repellency. / 4 to 8/2 is more preferable.

The catalyst layer 11 may contain a water repellent agent from the viewpoint that the effect of suppressing flooding is enhanced.
Examples of the water repellent include copolymers of TFE and hexafluoropropylene, copolymers of TFE and perfluoro (alkyl vinyl ether), polytetrafluoroethylene (hereinafter referred to as PTFE), and the like. As the water repellent, a fluorine-containing polymer that can be dissolved in a solvent is preferable because the catalyst layer 11 can be easily subjected to water repellent treatment.
The amount of the water repellent agent is preferably 0.01 to 30% by mass in the catalyst layer (100% by mass).

Cathode catalyst layer:
Since the catalyst layer 11 of the cathode 14 contains the polymer (H) as a solid polymer electrolyte polymer, the high proton conductivity, oxygen permeability, and oxygen / nitrogen separation characteristics of the polymer (H) prevent oxygen reduction reaction at the cathode 14. Overvoltage is reduced, and as a result, the reaction rate is improved.

The amount of platinum contained in the catalyst layer 11 of the cathode 14 is preferably 0.05 to 0.6 mg / cm ² from the viewpoint of the optimum thickness for efficiently performing the electrode reaction, and the balance between the cost and performance of the raw material is preferable. From this point, 0.1 to 0.35 mg / cm ² is more preferable.
The catalyst layer 11 of the cathode 14 is formed at a temperature of 150 to 180 ° C. for 1 to 60 minutes in order to stabilize the higher order structure of the solid polymer electrolyte polymer in the catalyst layer 11 and to enhance the oxygen / nitrogen separation characteristics. It is preferable to heat-treat. The heat treatment may be performed immediately after the catalyst layer 11 is dried and formed, or may be performed after the membrane electrode assembly 10 is manufactured.

Anode catalyst layer:
The solid polymer electrolyte polymer contained in the catalyst layer 11 of the anode 13 is not particularly limited, but the polymer (H) may be used similarly to the catalyst layer 11 of the cathode 14, or the conventional polymer (1 ) May be used.

  The ion exchange capacity of the solid polymer electrolyte polymer contained in the catalyst layer 11 of the anode 13 is preferably 1.0 to 2.8 meq / g dry resin. When the ion exchange capacity is 1.0 meq / g dry resin or more, proton conductivity under low or no humidification conditions does not become too low. If the ion exchange capacity is 2.8 meq / g dry resin or less, the swelling degree of the solid polymer electrolyte polymer does not become too high. Therefore, the solid polymer electrolyte polymer is not dissolved in the humidified water. The ion exchange capacity is preferably 1.1 to 2.5 meq / g dry resin from the viewpoint that proton conductivity under low humidification or non-humidification conditions can be secured and excessive swelling does not occur. From a point suitable for humidification conditions, 1.6 to 2.2 meq / g dry resin is more preferable.

The amount of platinum contained in the catalyst layer 11 of the anode 13 is preferably 0.01 to 0.3 mg / cm ² from the viewpoint of the optimum thickness for efficiently performing the electrode reaction, and the balance between the cost and performance of the raw material is preferable. From this point, 0.05 to 0.2 mg / cm ² is more preferable.

(Gas diffusion layer)
The gas diffusion layer 12 has a function of uniformly diffusing gas in the catalyst layer 11 and a function as a current collector.
Examples of the gas diffusion layer 12 include carbon paper, carbon cloth, and carbon felt.
The gas diffusion layer 12 is preferably water repellent treated with PTFE or the like.

(Carbon layer)
The membrane electrode assembly 10 may have a carbon layer 16 between the catalyst layer 11 and the gas diffusion layer 12, as shown in FIG. By disposing the carbon layer 16, the gas diffusibility on the surface of the catalyst layer 11 is improved, and the power generation characteristics of the polymer electrolyte fuel cell are greatly improved.

The carbon layer 16 is a layer containing carbon and a nonionic fluorine-containing polymer.
As carbon, carbon nanofibers having a fiber diameter of 1 to 1000 nm and a fiber length of 1000 μm or less are preferable.
Examples of the nonionic fluorine-containing polymer include PTFE.

(Solid polymer electrolyte membrane)
The solid polymer electrolyte membrane 15 is an electrolyte membrane having an ion exchange resin as a main component. A membrane made of a single ion exchange resin may be used, or it may be reinforced by a reinforcing body.

  The ion exchange resin is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an ether-bonded oxygen atom), and repetition based on TFE. More preferred are a polymer comprising units and units (U7), a polymer comprising repeating units based on TFE and units (U6), or a polymer comprising repeating units based on TFE, units (U6) and units (U7). . The polymer having the unit (M6) has a softening temperature higher than that of a conventional ion exchange resin film and high flexibility, and thus has low electric resistance and higher heat resistance than that of a conventional ion exchange resin film. Even if it repeats the swelling in the wet state and the shrinkage in the dry state, it is difficult to break.

  The solid polymer electrolyte membrane 15 may contain one or more atoms selected from the group consisting of cerium and manganese in order to further improve the durability. Cerium and manganese decompose hydrogen peroxide, which is a causative substance that causes deterioration of the solid polymer electrolyte membrane 15. Cerium and manganese are preferably present as ions in the solid polymer electrolyte membrane 15, and may exist in any state in the solid polymer electrolyte membrane 15 as long as they are present as ions.

  The solid polymer electrolyte membrane 15 may contain silica and heteropolyacid (zirconium phosphate, phosphomolybdic acid, phosphotungstic acid, etc.) as a water retention agent for preventing drying.

The thickness of the solid polymer electrolyte membrane 15 is preferably 5 to 30 μm, and more preferably 10 to 25 μm. If the thickness of the solid polymer electrolyte membrane 15 is 30 μm or less, a decrease in power generation characteristics of the solid polymer fuel cell under low or no humidification conditions can be further suppressed. Moreover, if the thickness of the solid polymer electrolyte membrane 15 is 5 μm or more, gas leakage and electrical short circuit can be suppressed.
The thickness of the solid polymer electrolyte membrane 15 is measured by observing the cross section of the solid polymer electrolyte membrane 15 with an SEM or the like.

  The ion exchange capacity of the ion exchange resin contained in the solid polymer electrolyte membrane 15 is preferably 0.9 to 2.5 meq / g dry resin. When the ion exchange capacity is 0.9 meq / g dry resin or more, the proton conductivity of the membrane under low or no humidification conditions does not become too low. If the ion exchange capacity is 2.5 meq / g dry resin or less, the degree of swelling of the solid polymer electrolyte membrane 15 does not become too high, and the dimensional change does not become too great. As a result, separation from the catalyst layer 11 is difficult to occur, and wrinkles are hardly generated in the cell inside the cell. The ion exchange capacity is preferably 1.1 to 2.0 meq / g dry resin from the viewpoint that proton conductivity under low humidification or non-humidification conditions can be secured and excessive dimensional change does not occur. From a point suitable for non-humidified conditions, 1.3 to 1.8 meq / g dry resin is more preferable.

(Method for producing membrane electrode assembly)
The membrane electrode assembly 10 is manufactured, for example, by the following method.
(A-1) A method in which the catalyst layer 11 is formed on the solid polymer electrolyte membrane 15 to form a membrane catalyst layer assembly, and the membrane catalyst layer assembly is sandwiched between the gas diffusion layers 12.
(A-2) A method in which the catalyst layer 11 is formed on the gas diffusion layer 12 to form electrodes (anode 13 and cathode 14), and the solid polymer electrolyte membrane 15 is sandwiched between the electrodes.

When membrane electrode assembly 10 has carbon layer 16, membrane electrode assembly 10 is manufactured by the following method, for example.
(B-1) A dispersion containing carbon and a nonionic fluorine-containing polymer is applied on a base film and dried to form a carbon layer 16, and a catalyst layer 11 is formed on the carbon layer 16. A method in which the layer 11 and the solid polymer electrolyte membrane 15 are bonded together, the base film is peeled off to form a membrane catalyst layer assembly having the carbon layer 16, and the membrane catalyst layer assembly is sandwiched between the gas diffusion layers 12.
(B-2) A dispersion containing carbon and a nonionic fluorine-containing polymer is applied onto the gas diffusion layer 12 and dried to form a carbon layer 16, and the membrane catalyst layer bonding in the method (a-1) A method of sandwiching a body with a gas diffusion layer 12 having a carbon layer 16.

Examples of the method for forming the catalyst layer 11 include the following methods.
(Y-1) A method of applying the catalyst layer forming liquid on the solid polymer electrolyte membrane 15, the gas diffusion layer 12, or the carbon layer 16 and drying it.
(Y-2) A method in which a catalyst layer forming solution is applied onto a base film, dried to form a catalyst layer 11, and the catalyst layer 11 is transferred onto a solid polymer electrolyte membrane 15.

The catalyst layer forming liquid is a liquid in which a solid polymer electrolyte polymer and a catalyst are dispersed in a dispersion medium. The catalyst layer forming liquid can be prepared, for example, by mixing the solid polymer electrolyte polymer in the present invention with a liquid composition and a catalyst dispersion.
Since the viscosity of the catalyst layer forming liquid varies depending on the method of forming the catalyst layer 11, it may be a dispersion of about several tens of cP or a paste of about 20000 cP.
The catalyst layer forming liquid may contain a thickener in order to adjust the viscosity. Examples of the thickener include ethyl cellulose, methyl cellulose, cellosolve thickener, and fluorine-based solvent (pentafluoropropanol, chlorofluorocarbon, etc.).

(Function and effect)
The membrane electrode assembly 10 described above uses a solid polymer electrolyte polymer having a high ion exchange capacity, a high oxygen permeability, and a high oxygen / nitrogen separation property for the cathode catalyst layer. Etc.) is high. In particular, it can contribute to simplification of the humidification system because it can exhibit high power generation performance even under low or no humidification conditions.

That is, the catalyst layer 11 of the cathode 14 was a dry polymer having an ion exchange capacity of 0.9 to 2.5 meq / g as a solid polymer electrolyte polymer, and was measured at a temperature of 100 ° C. by a high vacuum method. A polymer (H) having an oxygen permeability coefficient of 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more and an oxygen / nitrogen separation coefficient at 100 ° C. of 2.5 or more. Therefore, the polymer (H) efficiently supplies oxygen to the reaction field while excluding nitrogen, thereby improving the reaction activity and improving the power generation characteristics. In particular, the power generation characteristics under high temperature and low or no humidification conditions can be improved.

<Solid polymer fuel cell>
The membrane electrode assembly of the present invention is used for a polymer electrolyte fuel cell. A polymer electrolyte fuel cell is manufactured, for example, by forming a cell by sandwiching a membrane electrode assembly between two separators and stacking a plurality of cells.
Examples of the separator include a conductive carbon plate in which a groove serving as a passage for an oxidant gas (air, oxygen, etc.) containing fuel gas or oxygen is formed.

  Examples of the polymer electrolyte fuel cell include a hydrogen / oxygen fuel cell and a direct methanol fuel cell (DMFC). The methanol or methanol aqueous solution used for the DMFC fuel may be a liquid feed or a gas feed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the technical scope of this invention is not limited to this.

(Ion exchange capacity)
The ion exchange capacity of the solid polymer electrolyte polymer was determined by the following method.
The polymer was put in a glove box and left to dry for 24 hours or more in an atmosphere of flowing dry nitrogen. The dry mass of the polymer was measured in the glove box.
The polymer was immersed in a 2 mol / L sodium chloride aqueous solution, allowed to stand at 60 ° C. for 1 hour, and then cooled to room temperature. The aqueous solution of sodium chloride in which the polymer was immersed was titrated with a 0.5 mol / L aqueous solution of sodium hydroxide to determine the ion exchange capacity of the polymer.

(Monomer (a))
Compound (M1-1):

  Compound (M4-1):

(Monomer (b))
Synthesis of compound (M5-1):
P. Of International Publication No. 2003/037885 pamphlet. Compound (M5-1) was synthesized according to the method described in Examples 37-42.

(Monomer (c))
Synthesis of compound (M6-12):
Compound (M6-12) was synthesized according to the method described in Example 1 of JP-A-2008-202039.

  Compound (M7-11):

(Radical initiator)
Compound (i-1):
((CH ₃ ) ₂ CHOCOO) ₂ (i-1).
Compound (i-2):

Compound (i-3):
_{(C 3 F 7 COO) 2} ··· (i-3).

(solvent)
Compound (s-1):
CClF ₂ CF ₂ CHClF (s-1).
Compound (s-2):
CH ₃ CCl ₂ F (s-2).

[Example 1]
A stainless steel autoclave with an internal volume of 230 mL was charged with 31.00 g of the compound (M1-1), 214.5 g of the compound (M7-11) and 80 mg of the compound (i-1), and sufficiently removed under cooling with liquid nitrogen. I worried. Thereafter, 7.24 g of TFE was charged, the temperature was raised to 40 ° C., and the mixture was stirred for 24 hours, and then the reaction was stopped by cooling the autoclave.
After diluting the product with the compound (s-1), n-hexane was added thereto, and the polymer was aggregated and filtered. Thereafter, the polymer was stirred in compound (s-1), re-agglomerated with n-hexane, and dried under reduced pressure at 80 ° C. overnight to obtain polymer (F-1). Yield was 41 g.

^When the composition of the polymer (F-1) was determined by ¹⁹ F-NMR, the repeating unit based on TFE / the unit (U1-1) / the repeating unit based on the compound (M7-11) = 31/47/22 (molar ratio). The ratio of the repeating unit having a cyclic structure in the polymer (F-1) was 47 mol%.

By immersing the polymer (F-1) in an aqueous solution containing 20% by mass of methanol and 15% by mass of potassium hydroxide for 40 hours, the —SO ₂ F group in the polymer (F-1) is hydrolyzed, and convert these groups to -SO ₃ K groups. Then, the polymer was immersed in a 3 mol / L hydrochloric acid aqueous solution for 2 hours. The hydrochloric acid aqueous solution was exchanged, and the same treatment was repeated four more times to obtain a polymer (H-1) in which —SO ₃ K groups in the polymer were converted to sulfonic acid groups. The polymer (H-1) was thoroughly washed with ultrapure water. When the ion exchange capacity of the polymer (H-1) was measured, the ion exchange capacity was 0.94 meq / g dry resin.

  A mixed solvent of ethanol and water (ethanol / water = 70/30 mass ratio) is added to the polymer (H-1), the solid content concentration is adjusted to 15 mass%, and the mixture is stirred at 125 ° C. for 8 hours using an autoclave. did. Further, water was added to adjust the solid content concentration to 7.0% by mass to obtain a liquid composition (E-1) in which the polymer (H-1) was dispersed in a dispersion medium. The composition of the dispersion medium was ethanol / water = 35/65 (mass ratio).

  The liquid composition (E-1) was coated on an ETFE sheet with a die coater, dried at 80 ° C. for 30 minutes, further subjected to heat treatment at 165 ° C. for 30 minutes, and a cast film for gas permeability measurement having a thickness of 30 μm was formed. Formed. The oxygen permeability coefficient and the nitrogen permeability coefficient at 100 ° C. of the obtained cast film were measured using a high vacuum gas permeation apparatus. The results are shown in Table 1.

[Example 2]
39 g of water was added to 10 g of a supported catalyst in which 50% by mass of platinum was supported on carbon powder, and ultrasonic waves were applied for 10 minutes to obtain a catalyst dispersion. 60 g of the liquid composition (E-1) was added to the catalyst dispersion, and 64 g of ethanol was further added to adjust the solid concentration to 8% by mass to obtain a catalyst layer forming solution. The solution was applied onto a separately prepared sheet of ethylene and TFE copolymer (trade name: Aflex 100N, manufactured by Asahi Glass Co., Ltd., thickness 100 μm) (hereinafter referred to as ETFE sheet) at 80 ° C. It was dried for 30 minutes and further subjected to a heat treatment at 165 ° C. for 30 minutes to form a catalyst layer with a platinum amount of 0.35 mg / cm ² .

A stainless steel autoclave having an internal volume of 125 mL was charged with 45.9 g of the compound (M6-12), 16.5 g of the compound (s-1) and 12.65 mg of the compound (i-1), and cooled with liquid nitrogen. I was deaerated well. Thereafter, the temperature was raised to 40 ° C., TFE was introduced into the system, and the pressure was maintained at 0.55 MPaG. After stirring at 40 ° C. for 4.3 hours, the gas in the system was purged and the autoclave was cooled to complete the reaction.
After the product was diluted with the compound (s-1), the compound (s-2) was added thereto, and the polymer was aggregated and filtered. Thereafter, the polymer was stirred in the compound (s-1), re-agglomerated with the compound (s-2), and dried under reduced pressure at 80 ° C. overnight to obtain a polymer (F-2). The yield was 6.5g.

Using the polymer (F-2), a polymer (H-2) was obtained in the same manner as described above.
When the ion exchange capacity of the polymer (H-2) was measured, the ion exchange capacity was 1.51 meq / g dry resin.

  A mixed solvent of ethanol, water and 1-butanol (ethanol / water / 1-butanol = 35/50/15 mass ratio) is added to the polymer (H-2), the solid content concentration is adjusted to 15 mass%, and the autoclave And stirred at 125 ° C. for 8 hours. Water was further added to adjust the solid content concentration to 9% by mass to obtain a liquid composition (E-2) in which the polymer (H-2) was dispersed in a dispersion medium. The composition of the dispersion medium was ethanol / water / 1-butanol = 20/70/10 (mass ratio).

  The liquid composition (E-2) was coated on an ETFE sheet with a die coater, dried at 80 ° C. for 30 minutes, and further subjected to heat treatment at 190 ° C. for 30 minutes to form a solid polymer electrolyte membrane having a thickness of 20 μm. .

After peeling the ETFE sheet from the solid polymer electrolyte membrane, the solid polymer electrolyte membrane is sandwiched between two catalyst layers with an ETFE sheet, and heated and pressed under the conditions of a press temperature of 160 ° C., a press time of 5 minutes, and a pressure of 3 MPa, The catalyst layer was bonded to both surfaces of the solid polymer electrolyte membrane, and the ETFE sheet was peeled from the catalyst layer to obtain a membrane catalyst layer assembly having an electrode area of 25 cm ² .

A carbon layer made of carbon and PTFE was formed on the gas diffusion layer made of carbon paper.
The membrane / catalyst layer assembly was sandwiched between the gas diffusion layers so that the carbon layer and the catalyst layer were in contact with each other to obtain a membrane / electrode assembly.

The membrane electrode assembly was incorporated into a power generation cell, and power generation characteristics were evaluated under the following conditions.
Hydrogen (utilization rate 50%) was supplied to the anode of the membrane electrode assembly, and air (utilization rate 50%) was pressurized to 175 kPa (absolute pressure) and supplied to the cathode. Hydrogen and air were supplied without being humidified, and the current density was constant at 1.0 A / cm ² and increased from 80 ° C. The temperature at which the power generation voltage decreased with increasing temperature and the voltage decreased to 0.5 V was recorded. The results are shown in Table 1.

[Example 3]
A stainless autoclave having an internal volume of 1005 mL was charged with 30.36 g of the compound (M5-1), 665.8 g of the compound (s-1), 279 mg of methanol, and 36.8 mg of the compound (i-1), and liquid nitrogen. Degassed sufficiently under cooling by Then, after raising the temperature to 40 ° C., 45.8 g of TFE was charged and stirred for 5 hours, and then the reaction was stopped by cooling the autoclave.
After diluting the product with the compound (s-1), n-hexane was added thereto, and the polymer was aggregated and filtered. Thereafter, the polymer was stirred in the compound (s-1), re-agglomerated with n-hexane, and dried under reduced pressure at 80 ° C. overnight to obtain a polymer (F-3). The yield was 22.8 g.

^When the composition of the polymer (F-3) was determined by ¹⁹ F-NMR, the repeating unit based on TFE / the repeating unit based on the compound (M5-1) = 67/33 (molar ratio), and the polymer (F-3 The ratio of the repeating unit having a cyclic structure was 33 mol%.

  A polymer (H-3) and a liquid composition (E-3) were obtained in the same manner as in Example 1 using the polymer (F-3). Moreover, when the ion exchange capacity of the polymer (H-3) was measured, the ion exchange capacity was 1.59 meq / g dry resin.

  In the same manner as in Example 1, a cast film for gas permeability measurement having a thickness of 30 μm was formed. The oxygen permeability coefficient and the nitrogen permeability coefficient at 100 ° C. of the obtained cast film were measured using a high vacuum gas permeation apparatus. The results are shown in Table 1.

[Example 4]
A membrane / electrode assembly was prepared in the same manner as in Example 2 except that the liquid composition (E-3) was used as the liquid composition to be added to the catalyst dispersion, and the power generation characteristics were measured under the same conditions as in Example 2. . The results are shown in Table 1.

[Example 5]
In a 125 mL stainless steel autoclave, 9.16 g of compound (M5-1), 5.67 g of compound (M4-1), 5.0 g of compound (s-1), and 2 of compound (i-2) .4 mg was charged and sufficiently deaerated under cooling with liquid nitrogen. Then, after heating up to 65 degreeC and stirring for 23.5 hours, the autoclave was cooled and reaction was stopped.
After diluting the product with the compound (s-1), n-hexane was added thereto, and the polymer was aggregated and filtered. Thereafter, the polymer was stirred in compound (s-1), re-agglomerated with n-hexane, and dried under reduced pressure at 80 ° C. overnight to obtain polymer (F-4). The yield was 6.35g. The ratio of the repeating unit having a cyclic structure in the polymer (F-4) is 100 mol%.

  A polymer (H-4) and a liquid composition (E-4) were obtained in the same manner as in Example 1 using the polymer (F-4). Moreover, when the ion exchange capacity of the polymer (H-4) was measured, the ion exchange capacity was 1.54 meq / g dry resin.

  A cast film for gas permeability measurement having a thickness of 30 μm is formed in the same manner as in Example 1. The oxygen permeability coefficient and nitrogen permeability coefficient at 100 ° C. of the obtained cast film were measured using a high vacuum gas permeation apparatus, and the results are shown in Table 1.

[Example 6]
A membrane / electrode assembly is produced in the same manner as in Example 2 except that the liquid composition (E-4) is used as the liquid composition to be added to the catalyst dispersion. The power generation characteristics were measured under the same conditions as in Example 2, and the results are shown in Table 1.

[Example 7]
Compound (M7-11) 49.64 g, compound (s-1) 28.22 g and compound (s-1) dissolved at a concentration of 3.2% by mass in a stainless steel autoclave having an internal volume of 125 mL ( 38.9 mg of i-3) was charged and sufficiently deaerated under cooling with liquid nitrogen. Thereafter, the temperature was raised to 30 ° C., TFE was introduced into the system, and the pressure was maintained at 0.37 MPaG. After stirring for 4.8 hours, the reaction was stopped by cooling the autoclave.
After the product was diluted with the compound (s-1), the compound (s-2) was added thereto, and the polymer was aggregated and filtered. Thereafter, the polymer was stirred in the compound (s-1), re-agglomerated with the compound (s-2), and dried under reduced pressure at 80 ° C. overnight to obtain a polymer (F-5). Yield was 15.0 g.

    A polymer (H-5) and a liquid composition (E-5) were obtained in the same manner as in Example 1 using the polymer (F-5). Moreover, when the ion exchange capacity of the polymer (H-5) was measured, the ion exchange capacity was 1.10 meq / g dry resin.

  In the same manner as in Example 1, a cast film for gas permeability measurement having a thickness of 30 μm was formed. The oxygen permeability coefficient and the nitrogen permeability coefficient at 100 ° C. of the obtained cast film were measured using a high vacuum gas permeation apparatus. The results are shown in Table 1.

[Example 8]
A membrane / electrode assembly was produced in the same manner as in Example 2 except that the liquid composition (E-5) was used as the liquid composition to be added to the catalyst dispersion. The power generation characteristics were measured under the same conditions as in Example 2. The results are shown in Table 1.

  The membrane electrode assembly of the present invention is useful as a membrane electrode assembly that can be used in a polymer electrolyte fuel cell that can be operated under a wide range of conditions such as high temperature and low humidification.

DESCRIPTION OF SYMBOLS 10 Membrane electrode assembly 11 Catalyst layer 12 Gas diffusion layer 13 Anode 14 Cathode 15 Solid polymer electrolyte membrane 16 Carbon layer

Claims (3)

An anode having a catalyst layer comprising a solid polyelectrolyte polymer;
A cathode having a catalyst layer comprising a solid polyelectrolyte polymer;
A polymer electrolyte membrane disposed between the anode and the cathode;
The cathode catalyst layer is a dry resin having an ion exchange capacity of 0.9 to 2.5 meq / g as the solid polymer electrolyte polymer, and the oxygen permeation measured at a temperature of 100 ° C. by a high vacuum method. It contains a polymer (H) having a coefficient of 1 × 10 ⁻¹² [cm ³ (Normal) · cm / cm ² · s · Pa] or more and an oxygen / nitrogen separation coefficient at 100 ° C. of 2.5 or more. A membrane electrode assembly for a polymer electrolyte fuel cell characterized by the above.   The polymer (H) has a cyclic structure and a repeating unit (A) having no ion exchange group or a precursor group thereof, and / or a cyclic structure and an ion exchange group or a precursor group thereof. The total proportion of the repeating unit (A) and the repeating unit (B) is 20 mol% or more, of all repeating units in the polymer (H). Item 2. The membrane electrode assembly for a polymer electrolyte fuel cell according to Item 1.   The membrane electrode assembly for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the cathode catalyst layer is heat-treated at a temperature of 150 to 180 ° C for 1 to 60 minutes.

Images